Carburetor arrangement

ABSTRACT

The invention relates to a carburetor arrangement for an internal combustion engine ( 1 ) which drives a work apparatus. The engine ( 1 ) has an intake channel ( 3 ) leading through a carburetor ( 2 ). The intake channel ( 3 ) includes an intake opening ( 4 ) on the side of the carburetor ( 2 ) facing away from the engine ( 1 ). A baffle wall ( 5 ) is provided and covers the intake opening ( 4 ) at least partially. The baffle wall ( 5 ) is mounted transversely to the longitudinal axis ( 6 ) of the intake channel ( 3 ) at a spacing to the intake opening ( 4 ). The baffle wall ( 5 ) and the intake opening ( 4 ) define a baffle enclosure ( 7 ) disposed therebetween. At least a first component part ( 8 ) of the baffle wall ( 5 ) is inclined with respect to the longitudinal axis ( 6 ) of the intake channel ( 3 ) in such a manner that fuel droplets ( 9 ), which exit from the intake channel ( 3 ) and which impinge on the first component part ( 8 ) of the baffle wall ( 5 ), form a fuel film ( 10 ).

RELATED APPLICATION

[0001] This is a continuation-in-part application of patent applicationSer. No. 10/102,899 filed Mar. 22, 2002 and claiming priority of Germanpatent application 101 14 420.2, filed Mar. 23, 2001.

BACKGROUND OF THE INVENTION

[0002] A carburetor is provided in internal combustion engines fordriving work apparatus such as chain saws, blower/vacuum apparatus,brushcutters or the like. The carburetor has an intake channel via whichcombustion air is inducted. In the carburetor, an air/fuel mixture isprepared and, in two-stroke engines, is supplied to the crankcase of aninternal combustion engine. The intake operation is discontinuousbecause the intake stroke of an engine lies only approximately in theregion smaller than a half crankshaft rotation. During this time, thepiston of a two-stroke engine clears an inlet window via which theair/fuel mixture flows into the crankcase. After the end of the intakeoperation, the piston closes the inlet window so that the intakeoperation is interrupted. Comparable conditions arise in a four-strokeengine because of the opening and closing of the connection between thecylinder and the intake channel by means of a valve.

[0003] A pressure wave develops reflecting at the closed inlet windowbecause of the inertial and elasticity forces of the column of theair/fuel mixture which is accelerated in the intake direction in theintake channel. The pressure wave runs opposite to the intake directionthrough the intake channel. This pressure wave can run up to the intakeopening of the intake channel at the air filter end especially for afully open position of the throttle flap in the carburetor and canpropagate, for example, in the interior space of an air filter housingconnected ahead. Fuel droplets of the air/fuel mixture, which is formedin the carburetor, can be entrained by this pressure wave opposite tothe intake direction and be transported out of the intake channel. Thefuel portion, which reaches the interior space of the air filter, leadsthere to coking which restricts the capacity of the air filter or leadsto a deposit of solid particles on the outer side of the filtermaterial. The intake opening of the intake channel forms an open,likewise reflection capable end for the vapor column in the intakechannel. The vapor column can oscillate in the intake channel and, at aspecific rpm, resonance can occur which amplifies the unwanted effect ofthe fuel discharge.

[0004] To avoid the intake of fuel into the air filter housing,carburetor arrangements are known wherein a baffle wall is mounted at aspacing ahead of the intake opening. The baffle wall covers at least aportion of the intake opening. The pressure wave, which exits from theintake opening, is partially reflected by the baffle wall and is thrownback into the intake channel together with the entrained fuel droplets.These droplets cannot be braked without deceleration because of therelatively high specific weight of the fuel droplets compared to airwhereby a portion of the fuel droplets impinges upon the baffle wall andthere runs down. However, it has been shown that the impinging fueldroplets tend to burst upon impact and the resulting smaller fueldroplets are entrained by a part of the pressure wave past the bafflewall and into the interior space of the air filter housing.

SUMMARY OF THE INVENTION

[0005] It is an object of the invention to improve a known carburetorarrangement so that the entry of fuel into the air filter housing isminimized.

[0006] The carburetor arrangement of the invention is for an internalcombustion engine driving a work apparatus. The carburetor arrangementincludes: a carburetor; an intake channel defining a longitudinal axisand being formed in the carburetor and having an end facing away fromthe engine; the intake channel having an intake opening at the end; abaffle wall at least partially covering the intake opening; the bafflewall being mounted transversely to the longitudinal axis and beingdisposed at a distance from the intake opening; the baffle walldelimiting a baffle enclosure disposed between the baffle wall and theintake opening; the baffle enclosure having an inflow opening forcombustion air and the inflow opening lying rotated by approximately 90°to the intake opening; the inflow opening having an edge lying away fromthe intake opening; and, a protective wall provided at the edge and theprotective wall extending partially over the baffle enclosure.

[0007] For this purpose, at least a first component piece of the bafflewall or the baffle wall as a whole is inclined into the baffle enclosureor receptacle at an angle of inclination with respect to thelongitudinal axis of the intake channel. To prevent fuel droplets, whichburst on the baffle wall notwithstanding the selected inclination, froma partial exiting from the inflow opening, a protective wall is providedat the edge of the inflow opening which lies facing away from the intakeopening. This protective wall partially engages over the baffle space. Afuel entry into the air filter housing can largely be avoided.

[0008] The protective wall extends essentially in the plane of theinflow opening. The free end section of the protective walladvantageously lies closer to the intake opening than the edge of theinclined component piece which edge lies inside the baffle space. Thefree end section is especially bent over in the direction toward theintake opening into the baffle enclosure.

[0009] The angle of inclination is advantageously so selected that thefuel droplets, which exit from the intake channel and are entrained bythe reflected pressure wave, hardly burst upon impact and deposit as afuel film on the baffle wall. This film of fuel can be conducted away ina defined manner from the baffle wall and again be introduced into theintake channel. In this way, a coking of the air filter is avoided and,at the same time, via the return of the fuel film from the baffle wallinto the intake channel, a loss of fuel is avoided.

[0010] In an advantageous embodiment of the invention, an end wall isprovided which connects the lower edge of the baffle wall to a furtherlower edge of the intake opening. The end wall is, relative to thedirection of gravity of the work apparatus (held in the usual operatingposition) disposed below the baffle wall. As a consequence of the above,the film of fuel can flow off from the baffle wall to the end wallsupported by gravity. At the end wall, the film of fuel is transportedback into the intake channel by the intake air flow which flows by.Suitably, the above-mentioned first component part of the baffle wall isinclined with respect to the longitudinal axis in the direction towardthe end wall in such a manner that the cross section of the baffle spaceexpands from the longitudinal axis in the direction of the end wall.Because of this kind of an alignment of the inclination angle, thekinetic energy of the fuel droplets, which exit from the intake opening,operates upon impact on the baffle wall with a component in thedirection of the end wall. This force component acts supportively on thefuel film in the direction of gravity so that an improvement of theconveyance of the fuel film in the direction of the end wall and fromthere into the intake channel is given without additional assistingmeans. The transition between the end wall and the baffle wall isconfigured so as to be rounded, whereby a defined air flow can form inthe round, which, in this region too, makes possible a clean conveyanceof the fuel film to avoid unwanted collection locations. The end wallextends advantageously uniformly and especially as a straight line intothe lower channel wall of the intake channel whereby the fuel film canbe carried into the intake channel with little resistance. Furthermore,the flow resistance for the inducted air is reduced in this manner.

[0011] In an advantageous further embodiment of the invention, a furtherwall is provided on each side of the baffle wall and the end wall andthese walls conjointly define a baffle receptacle having an inflowopening lying opposite to the end wall. With a baffle receptacle of thiskind, precisely defined flow conditions are given with simple means forthe intake operation as well as for the reflection operation. As aconsequence thereof, the induction resistance can be adjusted to be lowand the inclination of the baffle wall for film formation can beadjusted precisely in a defined manner. The above-mentioned side wallsdefine a rounded transition to the baffle wall and also to the end wallbecause a portion of the fuel film also can deposit on these walls. Thisregion of the fuel film can be removed in the rounds correspondinglywell by the intake air flow. In total, a further reduction of the intakeflow resistance can be achieved with the rounded configuration.

[0012] In an advantageous further embodiment, the baffle wall includes asecond component part which is inclined with respect to the longitudinalaxis for forming a fuel film. The angle of inclination of the secondcomponent part is so selected that the cross section of the bafflereceptacle expands in the direction of the inflow opening starting fromthe longitudinal axis. In this way, the situation is accounted for that,in the region of the inflow opening, the pressure wave, which exits fromthe intake channel, together with the entrained fuel droplets, has avelocity component at an angle to the longitudinal axis of the intakechannel in the direction of the inflow opening. The second componentpart is inclined oppositely to the first component part. The secondcomponent part leads, in this way, to a low angle of incidence of thefuel droplets also in this region whereby a formation of a film of fuelis facilitated also near the inflow opening. The above-mentionedcomponent parts of the baffle wall define an edge whereby a transitionregion is avoided wherein fuel droplets can impinge at an obtuse angle.The protective wall is so configured that, when viewed in plan towardthe inflow opening, the second component part of the baffle wall iscompletely overlapped by the protective wall. A back-pulsating gas flowis deflected by the second component part in a direction toward theprotective wall and from there, the gas flow is guided back to theintake opening of the intake channel. This can be advantageouslysupported by a corresponding flow-facilitating shape of the protectivewall.

[0013] Analytic and empirical investigations have shown that the effectof the reflecting droplet formation or a film formation on the bafflewall is essentially dependent upon two dimensionless characteristicnumbers, namely, the Reynolds number Re and the Laplace number La. Thesimilarity characteristic quantity Re describes the ratio of the dropletvelocity and the droplet diameter to the kinematic viscosity of thefuel. When fuel droplets impinge upon the baffle wall, the velocitycomponent, which is perpendicular to the baffle wall surface, issignificant. This velocity component is a function of the angle ofimpingement. The Reynolds number too is, accordingly, a function of theangle of inclination of the baffle wall. The similarity characteristicquantity La describes the inherent characteristics of the fuel dropletin that its diameter as well as its surface tension and substancedensity are set in relationship to the square of the fuel viscosity.More detailed investigations have shown that a film formation on thebaffle wall occurs when the Reynolds number is:

Re≦24×La ^(0.419).

[0014] To adjust an adequately small Reynolds number for gasoline asfuel, an inclination angle of the baffle wall (that is, of its twocomponent parts) of ≦70° has been shown to be suitable whereby a desiredfilm formation is ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will now be described with reference to thedrawings wherein:

[0016]FIG. 1 is a schematic overview diagram of an internal combustionengine having a carburetor and a baffle receptacle mounted ahead of thecarburetor;

[0017]FIG. 2 shows details of the baffle receptacle in FIG. 1 in crosssection; and,

[0018]FIG. 3 is a perspective view showing the configuration of thebaffle receptacle having the protective wall 40.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0019]FIG. 1 shows an internal combustion engine 1 in the form of asingle-cylinder two-stroke engine as a drive motor for a work apparatusnot shown in greater detail. A cylinder 21 is arranged on an enginehousing 23 and a piston is disposed in the cylinder 21 and drives acrankshaft having a fan wheel 24 about a crankshaft axis 25 via aconnecting rod. An exhaust-gas muffler 22 is provided laterally of thecylinder 21. An intake channel 3 is provided on the side of the cylinder21 which lies opposite the exhaust-gas muffler 22. A carburetor 2 forforming an air/fuel mixture is connected via the intake channel 3. Theintake channel 3 opens on the side of the carburetor 2 facing away fromthe engine 1 with an intake opening 4 into the interior space 31 of anair filter housing 30. A baffle receptacle 17 is provided in theinterior space 31 and has a baffle wall 5 lying transversely to thelongitudinal axis 6 of the intake channel 3 and is mounted at a spacingahead of the intake opening 4. The baffle wall 5 lies in a plane (FIG.2) approximately parallel to the plane 35 of the intake opening 4.

[0020] The direction of the gravity force is indicated by arrow 11.Referred to the gravity force direction 11, the engine 1 is shown in itsusual operating position wherein the work apparatus, which is driventhereby, is held or guided, for example, at a handle. The lower edges(12, 13) are each referred to the gravity force direction 11. The edge12 of the baffle wall 5 and the lower edge 13 of the intake opening 4are connected to each other by the end wall 14. It can also be practicalto provide, for example, a fuel collecting device in lieu of the endwall 14 for a return of fuel into the fuel tank. A baffle receptacle 17is formed from the baffle wall 5 and the end wall 14 together withadditional side walls 16 shown in FIG. 2. The baffle receptacle 17 hasan inflow opening 18 on its side lying opposite the end wall 14. Theinflow opening 18 lies rotated by approximately 90° to the intakeopening 4. The engine 1 draws combustion air via the intake channel 3 inthe direction of arrow 27. The combustion air is drawn from the innerspace 31 of the air filter housing 30 in the direction of arrow 26through the inflow opening 18 into a baffle receptacle 7 between thebaffle wall 5 and the intake opening 4 and, from there, through theintake opening 4 into the intake channel 3.

[0021]FIG. 2 shows details of the baffle receptacle 17 of FIG. 1. Thebaffle receptacle 17 is shown in FIG. 2 as a mirror image compared toFIG. 1. The baffle receptacle 7 is delimited by a baffle wall 5, an endwall 14 and two side walls 16. Because of the cross sectional view, onlyone of the two side walls 16 is shown. The baffle wall 5 is subdividedinto a first component part 8 and a second component part 19, which joinone another in the region of an edge 20 lying inside the bafflereceptacle 7. Referred to the gravity force direction 11, the edge 20lies above the longitudinal axis 6 of the intake channel 3 and is closerto the plane 35 of the intake opening 4 than the foot section of thecomponent part 8 of the baffle wall 5 which joins to the end wall 14.The two component parts (8, 19) are inclined at respective inclinationangles (γ1, γ2) referred to the longitudinal axis or at angles (β1, β2)which are complementary to respective inclination angles (γ1, γ2).

[0022] In the embodiment shown and in adaptation to the substancecharacteristics of gasoline, angle γ1 is approximately 70° and angle γ2is approximately 60° and the corresponding complementary angles β1 andβ2 therefore amount to approximately 110° and 120°, respectively.Depending upon the application, also a smaller angle of inclination (γ1,γ2) can be practical. The selection of another fuel having differentsubstance characteristics, such as methanol, can lead to another angleof inclination (γ1, γ2) which effects the film formation.

[0023] Depending upon the application, a proportionately largerconfiguration of the first component part or of the second componentpart can be practical. Variations are also possible wherein the entirebaffle wall 5 comprises a first component part 8 or a second componentpart 19 and these component parts (8, 19) are inclined by correspondinginclination angles (γ1, γ2) with respect to the longitudinal axis 6.

[0024] The inclination of the first component part 8 at the inclinationangle γ1 is so aligned that the cross section of the baffle receptacle 7expands in the direction toward the end wall 14 starting from thelongitudinal axis 6. The inclination of the second component part 19 isoppositely aligned by the inclination angle γ2. Accordingly, the crosssection of the baffle receptacle 7 widens measured from the longitudinalaxis 6 starting from the edge 20 in the direction toward the inflowopening 18.

[0025] At the lower edge 12 of the baffle wall 5 (or the first componentpart 8 thereof), the baffle wall 5 extends rounded into the end wall 14.The transition between the baffle wall 5 and the side wall 16 and thetransition between the end wall 14 and the side wall 16 are alsoconfigured so as to be rounded in the region of arrow 32. The end wall14 extends in a straight line into the lower channel wall 15 in theregion of the lower edge 13 of the intake opening 4. Another uniformtransition, which avoids the steps, such as a curved transition, canalso be practical.

[0026] An exemplary fuel droplet 9 moves approximately parallel to thelongitudinal axis 6 of the intake channel 3 in the direction of arrow28. From the inclination angle γ1 of the first component part 8, thereresults, for the fuel droplet 9 shown, an impact angle α1 on the firstcomponent part 8, which is α1=γ1=70° in the embodiment shown, and leadsto the formation of a fuel film 10 on the first component part 8. Afurther fuel droplet 9 is shown in the region of the inflow opening 18and this fuel droplet 9 moves in the direction of arrow 29. The arrow 29has a component in the direction of the inflow opening 18. Because ofthe last-mentioned component, the angle of incidence α2 of this fueldroplet 9 on the second component part 19 is approximately 40° and istherefore less than γ2=60°. The incidence angle α2 is smaller incomparison to the first incidence angle α1 and leads to an improvedformation of the fuel film 10 on the second component part 19 to avoiddroplet formation in the vicinity of the inflow opening 18.

[0027] A protective wall 40 is provided in order to prevent a carryingout of fuel droplets or partial droplets through the inflow opening 18into the filter housing. The protective wall 40 is provided on the edge42 of the inflow opening 18 facing away from the intake opening 4. Asshown in FIG. 2, the protective wall 40 extends partially over thebaffle receptacle 7. The protective wall lies essentially at a distance43 from the plane of the inflow opening 18.

[0028] In order to reliably prevent a carrying away of the finest fueldroplets from the baffle receptacle 7, it is provided that the free endsection 41 of the protective wall 40 lies closer to the plane 35 of theintake opening than the edge 20 of the inclined first component part 8of the baffle wall 5. The edge 20 lies in the baffle receptacle 7. Thelength of the protective wall 40 is especially so provided that, in theplan view of the inflow opening 18, the protective wall 40 completelycovers the second component part 19 of the baffle wall 5. In this way,it is ensured that also fuel droplets 9, which impinge upon the secondcomponent part 19 of the baffle wall 5, are not carried away as a fuelfog through the inflow opening 18 in the case of a bursting; rather,these fuel droplets deposit on the protective wall 40. Gas, which flowsback from the intake channel 3, is deflected upwardly in the directiontoward the protective wall 40 because of the inclined position of thesecond component part 19 and is deflected back from the protective wall40 in the direction toward the intake opening 4. Here, it isadvantageous when the free end section 41 of the protective wall 40 isbent over preferably into the baffle receptacle 7 in a direction towardthe intake opening 4. An end section 41′, which is bent over in thismanner, can be configured also by a heaping of material in the region ofthe end section 41 and supports the back flow in the direction towardthe intake opening 4.

[0029] It is understood that the foregoing description is that of thepreferred embodiments of the invention and that various changes andmodifications may be made thereto without departing from the spirit andscope of the invention as defined in the appended claims.

What is claimed is:
 1. A carburetor arrangement for an internalcombustion engine driving a work apparatus, the carburetor arrangementcomprising: a carburetor; an intake channel defining a longitudinal axisand being formed in said carburetor and having an end facing away fromsaid engine; said intake channel having an intake opening at said end; abaffle wall at least partially covering said intake opening; said bafflewall being mounted transversely to said longitudinal axis and beingdisposed at a distance from said intake opening; said baffle walldelimiting a baffle enclosure disposed between said baffle wall and saidintake opening; said baffle enclosure having an inflow opening forcombustion air and said inflow opening lying rotated by approximately90° to said intake opening; said inflow opening having an edge lyingaway from said intake opening; and, a protective wall provided at saidedge and said protective wall extending partially over said baffleenclosure.
 2. The carburetor arrangement of claim 1, wherein said inflowopening defines a plane and said protective wall extends substantiallyin said plane.
 3. The carburetor arrangement of claim 1, wherein saidbaffle wall has a first component part defining an edge facing towardsaid intake opening; said intake opening defines a plane; and, saidprotective wall has a free end section lying closer to said plane ofsaid intake opening then said edge of said first component part of saidbaffle wall.
 4. The carburetor arrangement of claim 1, wherein saidprotective wall has a free end section bent over into said baffleenclosure in a direction toward said intake opening.
 5. The carburetorarrangement of claim 1, wherein said baffle wall has at least a firstcomponent part so inclined into said baffle enclosure at an angle (γ1)referred to said longitudinal axis.
 6. The carburetor arrangement ofclaim 5, wherein said angle (γ1) is so selected that fuel droplets,which exit from said intake channel and impinge on said first componentpart, form a film of fuel.
 7. The carburetor arrangement of claim 1,wherein said baffle wall has a lower edge and said intake channel has alower edge at said intake opening; said work apparatus has a usual workposition and said carburetor arrangement further comprises an end walllying downwardly in said work position referred to a direction definedby gravity force; and, said end wall connects said lower edge of saidbaffle wall to said lower edge of said intake opening.
 8. The carburetorarrangement of claim 7, wherein said baffle wall and said end wallextend one into the other over a rounded transition.
 9. The carburetorarrangement of claim 7, wherein said end wall extends uniformly into achannel wall of said intake channel.
 10. The carburetor arrangement ofclaim 9, wherein said end wall extends linearly into said intakechannel.
 11. The carburetor arrangement of claim 7, wherein said baffleenclosure includes two side walls; and, said side walls, said bafflewall and said end wall conjointly defining said baffle enclosure havingan in-flow opening lying opposite said end wall.
 12. The carburetorarrangement of claim 5, wherein said baffle wall has a second componentpart inclined at an inclination angle (γ2) with respect to saidlongitudinal axis which is so inclined that the cross section of saidbaffle enclosure expands from said longitudinal axis in a directiontoward said in-flow opening.
 13. The carburetor arrangement of claim 12,wherein said first component part and said second component part definean edge facing toward said intake opening whereat said second componentpart joins said first component part.
 14. The carburetor arrangement ofclaim 12, wherein the inclination angles (γ1, γ2) of each one of saidfirst and second component parts is equal to or less than approximately70°.